Method of preparing cellulose acetate films



Sept. 16, 1941. 5 ow ET AL 2,256,387

METHOD OF PREPARING CELLULOS-E ACETATE FILMS V Original FiIed March 18, 1929 ardfliarfow a2 1 v Siewari Carroll, gwvmt Patented Sept. 16, 1941 METHOD OF PREPARING CELLULOSE AGE- TATE FILMS Edward S. Farrow and Stewart J. Carroll, Rochester, N. Y., assignors, by mesne assignments, to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Original application March 18, 1929, Serial No. 347,813. Divided and this application June 14, 1930, Serial No. 461,115

1 Claim.

This invention relates to cellulose acetate films and particularly to a method of preparing such films.

This application is a division of our copending application Serial No. 347,813, filed March 18, 1929, which relates to cellulose ester films and particularly to a method of preparing such films. The present application relates more specifically to the incorporation of monochloronaphthalene into such films.

Cellulose acetate films have been prepared heretofore by coating a surface with a dope including cellulose acetate and a suitable solvent such as acetone. Certain softeners or plastifiers may be introduced to improve the quality of the film. The coating is dried in an oven or drier under uniform temperature conditions and is finally stripped from the surface. The procedure as described produces films which are generally satisfactory, but the operation consumes considerable time and is otherwise unadapted for economical commercial practice.

It is the object of the present invention to provide a more satisfactory method of preparing cellulose acetate films, together with a process of incorporating softeners or plastifiers therein.

We have discovered that the dope prepared by dissolving cellulose acetate in a suitable solvent, either with or without a softener or plastifier, may be hardened rapidly and effectively to produce a film when the thin layer on a supporting surface is subjected to the action of suitable agents which are non-solvents for cellulose acetate. The agents more suitable are highboiling compounds such as diamylphthalate. dibutylphthalate, amylbenzoate, ethylene glycol, tricresyl phosphate and monochloronaphthalene. Other organic compounds of similar character may be employed, but those mentioned are adapted to accomplish the purpose of the invention most effectively.

It is also very surprising that such high boiling compounds although they are non-solvents of the cellulose esters will diffuse into the cellulosic body and appear in the final product. This is not merely a surface effect but a penetration throughout the whole body of the material. Coagulation by these high boilers affords, then, a dual purpose of both congealing the dope and combining it with the plastic inducing agent.

In carrying out the method we prepare a dope by dissolving cellulose acetate in a solvent such as acetone, preferably in the proportions of one part by weight of the acetate to three to five parts of acetone. While the presence of a softener or plastifier is not essential, we prefer to add to the dope a suitable proportion of a softening agent, for example:

The dope, including the constituents mentioned, is spread in the form of a thin layer on a suitable polished surface and is immediately submerged in the hardening agent, which may comprise any one of the materials hereinbefore mentioned, or any equivalent thereof. As hereinbefore indicated, the hardening agents are generally high-boiling compounds which are non-solvents for cellulose acetate.

The coating sets quickly as a film which can be stripped generally from the supporting surface after a submergence of approximately twelve minutes. The time required will, of

course, vary with the particular composition and the hardening agent employed. As soon as the film is strip ed, it is passed rapidly through a washing bath consisting of a solvent for the hardening agent. Ethyl and methyl alcohols are suitable solvents but ethyl alcoholis preferred. The time required for washing does not exceed one-half to one minute. The film after washing is permitted to dry at somewhat above normal temperature i. e., approximately C. The drying may be accelerated by raising the temperature, but a higher temperature than that indicated is generally undesirable.

The film prepared by the method as described is clear and transparent and free from bubbles or other blemishes. It is flexible and is adapted to the usual applications of cellulose acetate films. It may be employed, for example, as a support for light-sensitive emulsions for photographic purposes.

The operation may be conducted in any suitable apparatus, an example of which is illustrated diagrammatically in the accompanying drawing.

Referring to the drawing, 5 indicates a revolving drum which may be rotated slowly by power applied from any suitable source. The

dope is prepared and is supplied to the drum from a container 6 in the form of a thin layer or tates, the film is carried therewith from the bath of hardening agent and may be stripped by a doctor 9. The film may be directed then over a roller H, into a receptacle 12 containing the washing liquid. It travels thence through rolls 1 3 which remove the surplus liquid. The film may be conducted then through a drying rack, comprising a succession of rollers, Hi from which it is withdrawn as a dried film ready for commercial use. The film may be rolled upon a suit able drum l5, which may be withdrawn from the apparatus at intervals carrying the finished film.

After operating the above apparatus for some time the solution in receptacle 8 gradually increases in the concentration of the film solvent and decreases in the concentration of the plasticizing agent. It is necessary, therefore, to maintain the amount of plastifier at a sufliciently high value to insure thorough coagulation. This may be accomplished by a constant flow of solvent stripped plastifier into and the contaminated plastifier out of receptacle 8. The flow as hereinabove enumerated are further apparent when ease of solvent recovery, freedom from solvent explosions, and other practical and economical improvements are realized. It is self evident that the recovery of the volatile solvents, by mere distillation from the other highboiling constituents of the coagulating bath, can

be more readily effected than the difiicult condensation of solvent vapors from a dilute gaseous vehicle. The less expensive apparatus required for distillation is considerable. Furthermore, the practical elimination of vapor explosions, which is ever present when dopes are coagulated in an air stream, is an advantage of far reaching importance.

Various changes may be made in the details of the procedure, and particularly in the selection of softening agents, plastifiers, and hardening agents, without departing from the invention or sacrificing any of its advantages.

Having thus described our invention, What we claim as new and desire to secure by Letters Patent is:

The method of rapidly seasoning sheets containing cellulose acetate which includes the steps of bathing in slightly diluted methanol and subsequently drying said sheets.

STEWART J. CARROLL. EDWARD S. FARROW. 

